Effects of Rabbit Serum on the Fine Structure of Mouse Pancreatic Acinar Cells in vitro

Abstract

Narrow (0.5 mm) pancreatic strips from BALB/c mice were incubated under a 95% O 2 + 5% CO 2 atmosphere at 37°C for 15, 30, 60, 120, and 180 min in fresh and in heat-inactivated, normal non-immunized rabbit serum.The acinar cells were then studied in an electron microscope after glutaraldehyde and osmium tetroxide fixation and Epon embedding.The ultrastructure of the acinar cells incubated in heat-inactivated serum remained essentially unaltered during the experiment.In fresh serum the early changes in the acinar cells were swelling of the granular endopla~mic reticulum and mitochondria.The plasma membrane was indistinct and discontinuous in many cells.Later, the acinar cells became necrotic.In these cells the endoplasmic reticulum was fragmented into dilated vacuoles and irregular cisternae.At this stage the mitochondrial matrix contained large dense granules.The zymogen granules were morphologically indistinguishable from normal even in the necrotic acinar cells.These results indicate that fresh rabbit serum is toxic to murine pancreatic acinar cells in vitro, and that rapid plasma membrane damage leading to cellular and cell organelle swelling and other degenerative changes, rather than zymogen activation and autodigestion, were the pathogenetic pathways of this complement- dependent cell injury.